1. Field of the Invention
The present invention relates to a master device, a slave device, etc., which perform connectionless communication.
2. Description of Related Art
Many industrial network systems are designed in the past, the industrial network systems contain slave devices performing data collection and control of the production device arranged in a workshop and a master device for managing a plurality of slave devices in a concentrating manner. The topology structure of the master device and the slave devices are diversified according to the production device subjected to the data collection and control of the slave devices or a relation of cooperation or wiring, etc., among the slave devices.
The master device and the slave devices perform the connectionless communication by means of EtherCAT (Ethernet for Control Automation Technology) (registered trademark). Besides, regarding the serial connection part of the topology structure of the master device and the slave devices, the frames containing the data to be sent are received and transmitted through reciprocation on one transmission path. Specifically speaking, the frames flowing to the transmission path from the master device arrive at the slave device at the terminal through the slave devices serially connected to the downstream of the master device. Then, the frames are retraced in the slave device at the terminal to return back to the master device from the slave devices according to the sequence opposite to the path to the slave devices.
Therefore, if the communication errors such as disconnection or damage to the frames and link disappearance are generated in the communication between the master device and the plurality of slave devices, the frames cannot return back to the side of the master device, and thus the slave machine causing the error cannot be judged.
In order to solve the problem, there is developed a technology: by controlling the opening and closing of the ports of the plurality of slave devices, whether the frames have returned is checked under the condition that each slave device is set to be the slave device of a network terminal, thereby detecting the connection abnormality of each slave device (patent document 1).